Dr. V.V MAHAJANI Professor of Chemical Engineering,

1. WET AIR OXIDATION Dr. V.V MAHAJANI Professor of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400 019 E.mail :vvm@udct.org vvmahajani@gmail.com Phone : (022) 2414 5616 (Extn2015) V V M 0

2. WELCOME TO ALL v.v.mahajani, uict

3. CHEMICAL PROCESS INDUSTRY ( CPI) BIRD’S EYEVIEW UTILITIES GASEOUS WASTE RAW MATERIALS PRODUCTS, By PRODUCTS, INTELLECTUAL SOLID WASTE INPUTSLIQUID WASTE (~ 90 % of water in) CPI V V M 1

4. Chemical Engineer’s View • BIO PROCESSESPHYSICO CHEMICAL PROCESSES • Aerobic 1. SEPARATION 3. BULK MINERALIZATION • Anaerobic Liquid / Liquid Extraction Incineration • Precipitation Wet Air Oxidation • Adsorption 4. POLISHING PROCESS • Membrane Photo Chemical • 2. REACTIVE DESTRUCTIONFenton • HydrotreatmentSonication • Ozonation • HYBRID PROCESSES : INNOVATIVE COMBINATION OF ALL V V M 2

5. PROCESS PRE-VIEW BIO-PROCESSES MOST POPULAR PROCESSES OPERATING AT NEAR ATM PRESSURE AND AMBIENT TEMPERATURE. BIO GAS GENERATION FROM SPENT WASH OF A DISTILLERY UNIT • LIMITATIONS SLOW RATES, LARGE VOLUME. HENCE, MORE FLOOR AREA REQD. OFTEN NEED ENGINEERED MICRO-ORGANISMS DO NOT PERMIT, INVARIABLY, SHOCK LOADS, TOXIC WASTES NEEDS ELABORATE POLISHING TREATMENT FOR WATER RECYCLE V V M 3

6. WATER COSERVATION RESULTS IN CONCENTRATED WASTE X NOT SUITABLE FOR BIO PROCESS • OPTIONS AVAILABLE: • INCINERATION • WET AIR OXIDATION V V M 4

7. INCINERATION : • HIGH OPERATING COST. • LOWER CAPITAL INVESTMENT.. • WATER CAN NOT BE RECYCLED UNLESS TREATED. • DEPRECIATION BENEFIT IS ONLY FOR CAPITAL • INVESTMENT AND NOT FOR OPERATING COST. V V M 5

8. WET AIR OXIDATION • MORE APPROPRIATELY : THERMAL PROCESS. • IT IS SUBCRITICAL OXIDATION PROCESS IN AN AQUEOUS MEDIUM WaterTc = 374 0C & Pc = 217.6 atm • OXIDATION OF ORGANIC INORGANIC SUBSTRATE IN PRESENCE OF MOLECULAR O2 T = 100 _ 250 0C; Pressure: O2 pressure 5 to 20 atm • O2 Solubility in water is minimum at near about 100oC. Above 100 oC it is increasing with increase in temperature. V V M 6

9. OXIDATION REACTIONFREE RADICAL MECHANISM O2 + H2O OH* via OH* radical formation NON SELECTIVE OXIDATION TO MINERALIZE OXIDIZABLE CONTAMINANTS ORGANICS O2 Ca Hb Nc Pd Xe Sf Og C CO2 H2O N N2, NH3, NO3, H H2O P PO4 X HX (halogen) S SO42- O2 O2 Inorganic substances O2 Na2S Na2SO4 Na2SO3 Na2SO4 V V M 7

10. OXIDATION POWER OF COMMON OXIDIZING AGENTSRELATIVE TO OXYGEN O2 1.00 Cl2 1.06 ClO2 1.06 HOCl 1.24 H2O2 1.48 O3 1.68 OH* (hydroxyl radical) 2.33 F2 2.50 V V M 8

11. HIGHER OXIDATION POWER MEANS A RELATIVE LACK OF • SELECTIVITY. • This property IS USELESS for organic synthesis but the most desirable in waste treatment. • SHE management does not allow use of “F” • WET Oxidation Technology is centered around OH* radical as non-selective but powerful oxidizing agent. V V M 9

12. INSIGHT INTO REACTION MECHANISM Large molecular wt O2 CO2 + H2O organic substrate low mol. wt organic acids (Acetic, Propionic, Glyoxalic, Oxalic) Complex Reactions Intermediates are formed and can be slow to oxidize or mineralize to CO2 V V M 10

13. KINETICS The waste is characterized as: BOD (bio-chemical oxygen demand), COD ( chemical oxygen demand ) & TOC ( total organic carbon ) Kinetics is presented in terms of COD / TOC reduction Instead of having complex kinetics representing series and parallel reactions, a series reaction approach is considered. We have found that a lumped parameter series reaction in terms of COD is more design friendly k1 k2 (COD) (COD) CO2 and H2O Original low mol. wt Waste intermediates In majority of cases, the second reaction step (k2) is the rate limiting step. V V M 11

14. The kinetics is then given as •  d(COD) = k (COD)m (O2)n dt m  1 ; n varies with 0.5 to 1.0 CATALYSTS Wet air oxidation reactions can be catalyzed by • homogeneous catalysts • heterogeneous catalysts to reduce SEVERITY of operating conditions. V V M 11

15. CATALYST CHARACTERIZATION • Homogeneous catalysts • The catalyst should be such that complete oxidation of substrate is possible to CO2 and H2O. • It should be compatible with MOC of the reactor. • It should be easily recoverable. CATALYST RECOVERY • Homogeneous catalysts could be recovered by • Precipitation • Ion exchange technique • Liquid emulsion membrane process • The leached catalyst and support can be recovered also by the above techniques. V V M 12

16. Heterogeneous catalysts • Cu, Co, Mn, Fe, Ru could be supported on suitable support such as Al2O3, SiO2 and TiO2 • Temperatures are around 200 oC and there exists acetic acid as an intermediate. This could result in extraction/leaching of the catalyst element into treated aqueous stream. • Leaching of support also may take place. We have observed: • Cu salts are very good for complete mineralization • Co and Fe are not able to oxidize acetic acid as effectively as copper V V M 13

17. Advantages and Limitations Advantages • It can handle concentrated waste COD 10,000-500,000 mg/l • It can handle toxic chemicals cyanides, sulphides and priority pollutants • Waste with high TDS can be handled • Energy integration possible • Very less space, even it can be underground. • Lower operating cost V V M 14

18. Limitations • Capital intensive due to exotic MOC. However, depreciation benefit makes it attractive! V V M 15

19. STEAM ENERGY RECOVERY SYSTEM AIR COMPRESSOR AIR BFW WET OXIDATION REACTOR AIR SATURATOR BFW EFFLUENT TREATED WATER ENERGY RECOVERY SYSTEM Typical Continuous Wet Oxidation System for Liquid Waste OFFGAS V V M 16

20. Integration with other waste treatment processes: It is possible to have hybrid systems to realize economic advantage of the waste treatment process. 1 Membrane – WAO 2 WAO - Membrane 3 Sonication – WAO 4 Fenton – WAO 5 Biological treatment – WAO 6 WAO - Biological treatment V V M 17

21. A SYSTEMATIC APPROACH FOR WATER TREATMENT FOR RECYCLE • We can use following guidelines for water recycle in a chemical plant • Identify contribution of water bill in the cost of production. • Identify the scenario around your project with special reference to availability of water in future, considering your future requirements due to expansion. • Take water balance in your plant. • Identify all water outlets such as plant effluent, utility blow downs, water used in administrative block, canteen etc. Please note that one can do little to evaporation loss in cooling tower. • Have detailed analysis of each effluent stream and decide which can be used for recycle and which can be used for purging. It may be possible to use purge water for gardening and horticulture. V V M 18

22. Have specifications for water use at all process blocks in the project. For instance, specifications for water used for washing filters would be totally different from that used as boiler feed water generating steam for captive power generation also. • Decide on treatment strategy. • Since each effluent stream is unique, carry out bench scale studies. • Carry out detailed technoeconomic feasibility study to ensure that set goals or targets could be achieved / realized. • Implement the project without any delays. ********************************************* V V M 19

23. SUSTAINABLE DEVELOPMENT OFMANKIND IS POSSIBLE ONLY WHEN WE LEARN TO RESPECT THE DIGNITY OF ENVIRONMENTAL PROTECTION